N.
I'm so sorry your son is going through that. How terrible! I agree with Melissa W. Keep calling that office until they can do something more for him. He shouldn't be in so much pain for so long. Can you at least give him some motrin?
My son has had a bad diaper rash a few times, but with a little A&D and Balmex or Boudreau's Butt Paste, it would clear up in a couple of days at most. Going several days with those horrible screams whenever you have to change their diaper would be unbearable. If you do get a call back from the nurse and they say there's nothing they can do, I would tell her I want to speak directly to the Pediatrician. Any good doctor will call you back themselves if you have a problem you really need to talk to them about.
Good luck to you. I hope your son can get some relief soon.